1. Field of the Invention
The present invention relates in general to a fluid-filled vibration damping device which exhibits a damping effect based on flows of a non-compressible fluid contained therein. More particularly, the invention is concerned with such a fluid-filled vibration damping device having an actuator for suitably controlling or changing damping characteristics of the vibration damping device, and a method of manufacturing the same.
2. Discussion of the Related Art
As one type of a vibration damping device adapted to damp input vibrations based on flows of a fluid contained therein or based on pressure change of the fluid, there is known a fluid-filled vibration damping device capable of controlling or changing its damping characteristics depending upon the input vibrations or other factors, as disclosed in JP-A-08-270718, JP-A-09-280304 and JP-A-05-149370. Such a fluid-filled vibration damping device, in general, includes: (a) a first mounting member; (b) a second mounting member spaced apart from the first mounting member in an axial direction of the second mounting member, and having a generally tubular shape and axially opposite open ends one of which is open toward the first mounting member; (c) an elastic body which elastically connects the first and second mounting members, and which fluid-tightly closes the above-described one of the axially opposite open ends of the second mounting member; (d) a movable member which is displaceable in the axial direction, and which fluid-tightly closes the other of the axially opposite open ends of the second mounting member so as to cooperate with the second mounting member and the elastic body to define a fluid-tight space filled with a non-compressible fluid; and (e) an actuator which displaces the movable member in the axial direction so as to control damping characteristics of the vibration damping device, and which is disposed outwardly of the other of the axially opposite open ends of the second mounting member.
In the above-described conventional vibration damping device, the actuator is attached to the second mounting member by caulking means, or other fixing means such as suitable bolts, as described in the above-described publications, so that the actuator is firmly fixed to a main body of the vibration damping device in which the first and second mounting members are connected by the elastic body to each other and the fluid-tight space filled with the non-compressible fluid is defined by the second mounting member and the elastic body.
For producing the vibration damping device in which the actuator is attached to the main body as described, it is necessary to perform a cumbersome operation such as caulking or a bolt-tightening operation, which would not be necessary if the vibration damping device were not equipped with the actuator. Such a cumbersome operation deteriorates efficiency of the production. Further, the caulking operation requires an exclusive installation or equipment to be performed or used, thereby increasing the production cost.
It is therefore a first object of the present invention to provide a fluid-filled vibration damping device having a simple construction which permits an actuator to be efficiently attached to its main body by a simple operation such as a press-fitting or drawing operation.
It is a second object of the invention to provide a method of manufacturing the fluid-filled vibration damping device.
The present invention provides a fluid-filled vibration damping device or a method of manufacturing the same according to each of the following aspects, preferred forms or advantageous arrangements of the invention. It is to be understood that the following aspects, preferred forms and advantageous arrangements are provided to facilitate the understanding of possible combinations of features recited in the following aspects, preferred forms and advantageous arrangements, and that the technical features and the combinations of the technical features disclosed in the present specification are not limited to the following aspects, preferred forms and advantageous arrangements, but should be recognized based on the overall description of the specification and the drawings.
The above first object may be achieved according to a first aspect of the present invention, which provides a fluid-filled vibration damping device comprising: (a) a first mounting member; (b) a second mounting member which has a generally tubular shape and which is spaced apart from the first mounting member in an axial direction of the second mounting member, the second mounting member having axially opposite open ends, one of which is open toward the first mounting member; (c) an elastic body which elastically connects the first and second mounting members, and which fluid-tightly closes the one of the axially opposite open ends of the second mounting member; (d) a movable member which is displaceable in the axial direction, and which fluid-tightly closes the other of the axially opposite open ends of the second mounting member so as to cooperate with the second mounting member and the elastic body to define a fluid-tight space filled with a non-compressible fluid; and (d) an actuator which displaces the movable member in the axial direction so as to control damping characteristics of the vibration damping device, and which is disposed on one of axially opposite sides of the second mounting member which is remote from the first mounting member; wherein the improvement comprises: the actuator being provided with a connector which connects the actuator with the second mounting member, the connector having a generally tubular shape and extending from the actuator in a direction toward the above-described one of the axially opposite open ends of the second mounting member, the connector being fitted on an outer circumferential surface of the second mounting member so that the actuator is fixed relative to the second mounting member.
In the fluid-filled vibration damping device constructed according to this first aspect of the invention, it is possible to fix the movable member in an axial portion of the second mounting member which is adjacent to the above-described other of the axially opposite open ends of the second mounting member, by press-fitting the movable member into the axial portion of the second mounting member, or by drawing or plastically deforming the axial portion of the second mounting member radially inwardly thereby forcing the axial portion onto the movable member. Thus, a main body of the vibration damping device, in which the fluid-tight space is defined by the second mounting member, the elastic body and the movable member, can be obtained by the press-fitting or drawing operation without a cumbersome caulking operation. Similarly, it is also possible to fix the actuator to the thus obtained main body, by a press-fitting or drawing operation without a caulking operation. Accordingly, the present vibration damping device advantageously eliminates a conventionally-required, cumbersome caulking operation in the production process and accordingly expensive equipment required for such caulking operation, whereby the production efficiency and cost of the present vibration damping device are remarkably improved and lowered, respectively.
The actuator defined in the present first aspect is not limited to any specific construction, but may be of, for example, a pneumatic actuator which has an enclosed air chamber partially defined by a wall member that is displaceable as a result of change of the pressure in the air chamber, so as to produce mechanical force based on the displacement of the wall member, or alternatively may be of an electromagnetic actuator which has an output member displaceable on the basis of an electromagnetic force or magnetic force. The damping characteristics of the vibration damping device may be controlled, for example, by alternately pressing and moving the movable member onto and away from an opening end of a fluid passage which is formed in the fluid-tight space so as to selectively open and close the fluid passage, or alternatively by oscillatingly displacing the movable member in the axial direction so as to control the pressure in the fluid-tight space.
According to a first preferred form of the first aspect of the invention, the actuator is fixed to the connector which is formed independently of the actuator. The independently formed connector may be fixed to the actuator by a simple pressing-fitting or drawing operation.
According to a second preferred form of the first aspect of the invention, the actuator includes a portion which is formed integrally with the connector.
According to a third preferred form of the first aspect of the invention, the movable member includes an elastic rubber sheet which is elastically deformable so as to be displaceable in the axial direction, and wherein the elastic rubber sheet is fixed at an outer periphery thereof to a fitting ring which is fitted in an inner circumferential surface of the second mounting member.
In the fluid-filled vibration damping device constructed according to the third preferred form of the first aspect of the invention, the movable member can be more easily attached in the above-described axial portion of the second mounting member, by a suitable press-fitting or drawing operation. The axial portion of the second mounting member is preferably covered at its inner circumferential surface with a seal layer which may be formed integrally with the elastic body or formed independently of the elastic body, so that the seal layer is radially interposed and gripped between and by the second mounting member and the fitting ring, whereby a degree of fluid-tightness of the fluid-tight space is advantageously increased.
According to a fourth preferred form of the first aspect of the invention, the second mounting member has, at the other of the axially opposite open ends, an annular engaging portion which extends radially inwardly from an inner circumferential surface of the second mounting member, and wherein the movable member is fixed at an outer circumferential surface thereof to a support member so as to be supported by the support member, displaceably relative to the second mounting member in the axial direction, the support member being disposed in an axial portion of the second mounting member which is located axially inwardly of the annular engaging portion, the support member being fitted in the axial portion by reduction of a diameter of the axial portion, so that the support member is fixed to the second mounting member.
Where the second mounting member is made of a metallic material, the annular engaging portion can be easily formed by plastically deforming or bending an axial end portion of the second mounting member inwardly in the radial direction. According to this fourth preferred form, the support member is more firmly fixed in the above-described axial portion of the second mounting member, owing to the annular engaging portion and the reduction of the diameter of the axial portion of the second mounting member.
According to a fifth preferred form of the first aspect of the invention, the fluid-filled vibration damping device further comprising a partition member fixedly disposed in the fluid-tight space so as to divide the fluid-tight space into a pressure-receiving chamber which is partially defined by the elastic body and which receives vibrations applied to the vibration damping device, and an equilibrium chamber which is partially defined by the movable member and whose volume is variable by displacement of the movable member, and wherein the partition member defines an orifice passage which communicates the pressure-receiving chamber and the equilibrium chamber and which has an open end open to the equilibrium chamber, and wherein the actuator displaces the movable member between an open position in which the movable member is spaced apart from the partition member to open the open end of the orifice passage, and a closed position in which the movable member is brought in contact with the partition member to close the open end, whereby the damping characteristics of the vibration damping device are controlled.
In the fluid-filled vibration damping device constructed according to this fifth preferred form, the damping characteristics of the vibration damping device can be controlled or changed by alternately opening and closing the orifice passage. The orifice passage may includes two orifice passages having respective ratios A/L which are different from each other, where xe2x80x9cAxe2x80x9d represents the cross sectional area of the passage while xe2x80x9cLxe2x80x9d represents the length of the passage. One of the two orifice passages, which has a larger ratio A/L than that of the other orifice passage, is selectively opened and closed, while the other orifice passage is held open, for selectively enabling or disabling the two orifice passages having the different ratios A/L, so that the vibration damping device exhibits a sufficiently high damping effect with respect to different frequency bands of the input vibrations.
According to a sixth preferred form of the first aspect of the invention, the actuator includes a rigid wall member, an elastic wall member which is opposed to the rigid wall member and is nearer to the first mounting member in the axial direction than the rigid wall member and which cooperates with the rigid wall member to define a working air chamber therebetween, a pressing member which is made of a hard material and which is fixed in a central portion of the elastic wall member, an annular fitting member which is fixed to an outer peripheral portion of the elastic wall member, and a biasing member which biases the pressing member in a direction away from the rigid wall member, wherein the working air chamber is connectable to a source of a vacuum pressure so that the pressing member is displaced in a direction toward the rigid wall member by suction of the vacuum pressure against a biasing force of the biasing member when the vacuum pressure is applied to the working air chamber, and wherein the annular fitting member is fitted in the connector so that the actuator is fixed to the connector.
According to a first advantageous arrangement of the sixth preferred form, the rigid wall member is formed integrally with the connector.
The actuator defined in the above sixth preferred form is preferably of a pneumatic actuator. The connector may be formed independently of the actuator, or alternatively may be formed integrally with a portion of the actuator. In the former case, the rigid wall member of the actuator may be fixed, for example, in an axially open end portion of the tubular-shaped connector. In the latter case, the rigid wall member of the actuator may be formed integrally with the connector, as described in the above first advantageous arrangement. That is, the tubular-shaped connector has, in its axially open end portion, a bottom wall which serves as the rigid wall member of the actuator. For fixing the actuator to the tubular-shaped connector, the annular fitting member of the actuator may be press-fitted in the connector, or may be fixed by caulking to the connector, or alternatively may be brought into engagement with a radial projection provided in the connector. The biasing member may include a coil spring disposed between the pressing member and the rigid wall member which are opposed in the axial direction.
According to a second advantageous arrangement of the sixth preferred form, the rigid wall member has, in a central portion thereof, a concave portion which is concave toward the elastic wall member, and an axial projection which projects from a bottom wall of the concave portion in a direction away from the elastic wall member and which has a through-hole for communication between the working air chamber and the exterior of the vibration damping device, the axial projection serving as a joint to which a conduit connected to the vacuum pressure source is connected, so that the vacuum pressure is applied to the working air chamber through the through-hole.
In the fluid-filled vibration damping device constructed according to this second advantageous arrangement of the sixth preferred form, the rigid wall member has the concave portion in the central portion, and the axial projection serving as the joint is provided in the bottom wall of the concave portion. According to this second arrangement, the joint does not have to protrude outwardly from the actuator or the vibration damping device, if the concave portion has a sufficiently large depth as measured in the axial direction. Further, the elastic wall member may have, in the central portion, a stop member which is made of an elastic material and which projects toward the bottom wall of the concave portion of the rigid wall member, so that the stop member is brought into abutting contact with the bottom wall of the concave portion so as to limit an amount of axial displacement of the pressing member toward the rigid wall member in a cushioning manner, when the pressing member is displaced in the direction toward the rigid wall member.
According to a seventh preferred form of the first aspect of the invention, the second mounting member has a flange portion which extends radially outwardly from the above-described one of the axially opposite open ends of the second mounting member, and wherein the connector is held in contact, at one of axially opposite open ends thereof remote from the actuator, with the flange portion of the second mounting member, so that the connector is held in a predetermined axial position relative to the second mounting member.
According to an eighth preferred form of the first aspect of the invention, the connector has a flange portion which extends radially outwardly from the above-described one of the axially opposite open ends of the connector, so that the connector is held in contact, at the flange portion of the connector, with the flange portion of the second mounting member.
In the fluid-filled vibration damping device constructed according to the above seventh preferred form, the connector is firmly held in the predetermined axial position relative to the second mounting member, owing to the simple mechanism, namely, by the abutting contact of the axial end of the connector with the flange portion of the second mounting member. The connector may have the flange portion in the axial end, as described in the above eighth preferred form, so that the connector is still more firmly held in the predetermined axial position relative to the second mounting member, by the abutting contact of the flange portions of the respective connector and second mounting member.
According to a ninth preferred form of the first aspect of the invention, the second mounting member has a fitting portion at which the second mounting member is fitted in the connector, and a small-diameter portion which has an outside diameter smaller than that of the fitting portion and which is axially nearer to the above-described other of the axially opposite open ends of the second mounting member, than the fitting portion.
In the fluid-filled vibration damping device constructed according to the ninth preferred form, the provision of the small-diameter portion in the second mounting member permits the second mounting member to be easily introduced into the tubular-shaped connector in an operation for assembling the actuator and the main body. The present ninth preferred form is advantageously carried out in combination with the above-described fourth preferred form in which the support member disposed in the axial portion of the second mounting member is fixed to the second mounting member by the reduction of the diameter of the axial portion. That is, the small-diameter portion is advantageously constituted by the axial portion whose diameter is reduced.
According to an advantageous arrangement of the ninth preferred form of the first aspect, the second mounting member further has a tapered portion which is located between the fitting portion and the small-diameter portion as viewed in the axial direction and which has an outside diameter that increases as the second mounting member extends in a direction away from the actuator toward the first mounting member.
If the second mounting member further has the tapered portion between the small-diameter and the fitting portion, as recited in this advantageous arrangement of the ninth preferred form, the second mounting member can be more easily introduced into the tubular-shaped connector, since the tapered portion facilitates entrance of the fitting portion into the connector, following entrance of the small-diameter portion into the connector.
The above second object may be achieved according to a second aspect of the present invention, which provides a method of manufacturing the fluid-filled vibration damping device defined in the above-described first aspect of the invention. The method comprises: (i) a step of preparing an integral intermediate assembly in which the first and second mounting members are bonded to the elastic body by vulcanization of an unvulcanized material to form said elastic body; (ii) a step of immersing the integral intermediate assembly and the movable member in a mass of the non-compressible fluid, and fitting the movable member into the second mounting member within the mass of the non-compressible fluid, so that the fluid-tight space is filled with the non-compressible fluid; (iii) a step of reducing a diameter of the second mounting member, such that the movable member is fixed to the second mounting member, and such that the other of the axially opposite open ends of the second mounting member is fluid-tightly closed; (iv) a step of preparing the actuator which is provided with the connector; and (v) a step of fitting the connector onto the outer circumferential surface of the second mounting member in an atmosphere, so that the actuator is fixed relative to the second mounting member.
According to the present method, the movable member can be attached to the integral intermediate assembly by the press-fitting or drawing operation, so that the main body of the vibration damping device can be obtained without a cumbersome caulking operation. Similarly, the actuator can be attached to the main body by the press-fitting or drawing operation without a caulking operation. Accordingly, the present method eliminates a conventionally-required, cumbersome caulking operation in the production process and accordingly expensive equipment required for such caulking operation, whereby the efficiency of the production and cost of the equipment for the production are remarkably improved and lowered, respectively.
According to a preferred form of the second aspect of the invention, the method comprises a step of fitting the connector onto the outer circumferential surface of the second mounting member, by successively introducing the small-diameter portion, the tapered portion and the fitting portion of the second mounting member in the order of description into the connector through one of axially opposite open ends of the connector which is remote from the actuator, so that the actuator is fixed relative to the second mounting member.